What action must be taken in the event of overheating bleed air?

When dealing with overheating bleed air, closing the associated engine bleed air shutoff valve is the necessary action. This step is crucial because when bleed air becomes too hot, it can indicate a malfunction or an unsafe condition that could lead to aircraft system failures or even engine damage. By shutting off the bleed air supply from the affected engine, you not only prevent further overheating but also protect critical systems from potential hazards.

Other actions, such as opening isolation valves or activating heat exchangers, do not directly address the immediate risk associated with the overheated air. Engaging a cooling turbine is also not an appropriate response in this scenario. Addressing the source of heat by shutting off the bleed is essential for maintaining safe and efficient operations in the aircraft.